Application of calcite, Mg-calcite, and dolomite as Raman pressure sensors for high-pressure, high-temperature studies

摘要

The Raman spectra of calcite, Mg-calcite, and dolomite were measured under ambient and high pressure-temperature (P-T) conditions using a hydrothermal diamond anvil cell, for the purpose of developing new pressure sensors suited for experiments investigating the physicochemical properties of carbonate minerals. By fitting the Raman vibrational frequencies as functions of pressure and temperature, pressure (P, in MPa) can be determined from relative frequency shifts (in cm(-1)) of the symmetric stretching (nu(1)) and librational (nu(L)) lattice vibrations of calcite: P = 229(1) x (nu(1 calcite, HP) - nu(1 calcite, ref)), P = 162(1) x (nu(L calcite, HP) - nu(L calcite, ref)), or from the translational (nu(T)) and librational (nu(L)) lattice vibrations of dolomite: P = 371(3) x [(nu(L dolomite, HP) - nu(T dolomite, HP)) - (nu(L dolomite, ref) - nu(T dolomite, ref))], where nu(ref) is the value under ambient P-T conditions. Under elevated temperatures, correction for the effect of temperature (T, in degrees C) on the Raman frequency shifts can be accomplished through nu(1 calcite, HT) = nu(1 calcite, ref) - 6.8(5) x 10(-6) x T-2-0.0051(3) x T + 0.12, nu(L calcite, HT) = nu(L calcite, ref) - 1.07(12) x 10(-5) x T-2-0.00341(7) x T + 0.76, nu(L dolomite, HT) - nu(T dolomite, HT) = (nu(L dolomite, ref) - nu(T dolomite, ref)) - 0.0198(3) x T + 0.45. Application of the calcite and dolomite Raman pressure sensors should be made on condition that no phase transitions or breakdown reactions occur under high P-T conditions, with errors of +/- 50 MPa and +/- 5% at pressures below and above 1.0 GPa, respectively. Results from an additional experiment showed that pressures determined using alternate Raman pressure calibration methods were self-consistent and in excellent agreement with the results determined using the nu(1) Raman peak shifts of aragonite.